pcDuino – I2C Test

sky-Hawk where

Today I connected up a my prototype board for an I2C experiment with the pcDuino. Blinky Lights!
Video of simple I2C parallel port test using Python.
http://player.youku.com/player.php/sid/XNTI3MDk1MTU2/v.swf


Using I2C
If you want to try interfacing with the pcDuino I2C yourself, you will need to install the software for using the I2C bus:

1. sudo apt-get install i2c-tools
   
2. sudo apt-get install python-smbus

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i2c-tools provides command line applications for checking and accessing i2c bus devices.

i2cdetect – scans an I2C bus for devices
i2cget – reads registers visible through the I2C bus
i2cset – writes registers visible through the I2C bus

python-smbus provides Python access to I2C (SMBus) devices.

Connecting PCF8574
Connect a PCF8574 I2C parallel port chip to the pcDuino I2C bus. For feedback, connect each of the outputs through resistors to LEDs. Be sure to connect power to 3.3 Vdc and GND. I connected the address select pins to ground (address 0×20). I can post a detailed wiring diagram if anyone is interested.

To verify your connections, use i2cdetect from the command line. It should show a single device at address 0×20 on bus 2 (the I2C bus available on the GPIO connectors).

i2cdetect -y 2
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Python
Python source code for testing the I2C bus will cycle the LEDs as shown in the video.

1. #! /usr/bin/env python
   
2. #######################################################################
   
3. # Simple I2C parallel port demostration Python class
   
4. # Originally developed for the pcDuino platform
   
5. #
   
6. # This class file may be included in other application to provide
   
7. # simple read and write support for i2c attached 8574 i2c parallel
   
8. # port.
   
9. #
   
10. # The connection will default to I2C Bus 2 - the default external I2C
    
11. # bus on the pcDuino. The default parallel port address is 0x20 - the
    
12. # first standard address for the 8574.
    
13. #
    
14. # If this file is executed, it will run a pattern demo output on the
    
15. # parallel port. Best viewed by having LEDs connected to the outputs.
    
16. #
    
17. # Enjoy!
    
18. # Bill
    
19. #######################################################################
    
20. # Copyright (c) 2013 by William Greathouse, Brecksville, OH, USA
    
21. #
    
22. # Permission is granted to use the source code within this
    
23. # file in whole or in part for any use, personal or commercial,
    
24. # without restriction or limitation.
    
25. #
    
26. # No warranties, either explicit or implied, are made as to the
    
27. # suitability of this code for any purpose. Use at your own risk.
    
28. #######################################################################
    
29. 
    
30. import sys
    
31. import smbus
    
32. import time
    
33. 
    
34. I2CBUS=2
    
35. PARADR=0x20
    
36. DELAY=0.05
    
37. 
    
38. class I2Cparallel:
    
39.   # initialize the i2c connection to the parallel port
    
40.   def __init__(self, adr=PARADR, bus=I2CBUS):
    
41.     self.bus=bus
    
42.     self.adr=adr
    
43.     self.i2c=smbus.SMBus()
    
44.     self.i2c.open(self.bus)
    
45.     # Set all outputs to high state (state required for input)
    
46.     # If this fails, chip is not responding on i2c bus
    
47.     try:
    
48.       self.i2c.write_byte(self.adr, 0xff)
    
49.     except:
    
50.       print "Unable to access parallel port on bus %d, addresss 0x%02x" % (self.bus, self.adr)
    
51.       sys.exit(1)
    
52. 
    
53.   # output value to parallel port
    
54.   def out_byte(self,value):
    
55.     self.i2c.write_byte(self.adr, value)
    
56. 
    
57.   # input value from parallel port
    
58.   def in_byte(self):
    
59.     return self.i2c.read_byte(self.adr)
    
60. 
    
61. if __name__=="__main__":
    
62.   # initialize the interface, passing just the address as an example
    
63.   parport=I2Cparallel(PARADR)
    
64. 
    
65.   # flash all output lines
    
66.   for _ in range(10):
    
67.     parport.out_byte(0x00)
    
68.     time.sleep(DELAY)
    
69.     parport.out_byte(0xff)
    
70.     time.sleep(DELAY)
    
71. 
    
72.   # Do a scanning display, single bit on
    
73.   for _ in range(10):
    
74.     for i in range(8):
    
75.       parport.out_byte(1<<i) time.sleep(delay)="" for="" i="" in="" range(8):="" parport.out_byte(0x80="">>i)
    
76.       time.sleep(DELAY)
    
77. 
    
78.   # Do a scanning display, single bit off
    
79.   for _ in range(10):
    
80.     for i in range(8):
    
81.       parport.out_byte(~(1<<i)) time.sleep(delay)="" for="" i="" in="" range(8):="" parport.out_byte(~(0x80="">>i))
    
82.       time.sleep(DELAY)
    
83. 
    
84.   # Set all outputs to high state (state required for input)
    
85.   parport.out_byte(0xff)

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sky-Hawk where

沙发。。。还是那句话，多看教学视频，屌丝终成高富帅。哈